## What is the meaning of Rayleigh number?

Rayleigh number is a dimensionless number that represents the ratio of buoyancy and thermal diffusivity.

## What is the critical Rayleigh number?

The critical rayleigh number corresponds to the take off of Vmax and it is approximatively egual to1800. Moreover, we think it is possible to perform the accuracy of this number for the same reasons as previously.

**What does Biot number represent?**

Biot number is a dimensionless number that represents the ratio of thermal convection from solid surface and thermal conduction from solid interior. It can be expressed in the following equation. Biot number indicates how fast heat can be transferred by thermal conduction.

**What is Rayleigh number formula?**

The Rayleigh number is simply defined as the product of the Grashof number, which describes the relationship between buoyancy and viscosity within a fluid, and the Prandtl number, which describes the relationship between momentum diffusivity and thermal diffusivity. Rax = Grx . Pr.

### What does a low Rayleigh number mean?

In fluid mechanics, the Rayleigh number (Ra) for a fluid is a dimensionless number associated with buoyancy-driven flow, also known as free or natural convection. It characterises the fluid’s flow regime: a value in a certain lower range denotes laminar flow; a value in a higher range, turbulent flow.

### Can you have a negative Rayleigh number?

It can’t. It will be negative if the Ts is lower than Tinf, and simply change the order for them.

**What does Schmidt number represent?**

The Schmidt number (Sc) is the ratio of the kinematic viscosity to the molecular diffusion coefficient, i.e., Sc= v/Dm. Based on a number of field studies, empirical equations which relate k to wind speed have been proposed.

**What is Biot and Fourier number?**

The Biot number is the ratio of the internal resistance of a body to heat conduction to its external resistance to heat convection. Therefore, a small Biot number represents small resistance to heat conduction, and thus small temperature gradients within the body.

#### What happens when Rayleigh number increases?

As Rayleigh number increases, the buoyancy forces increases and in turn thermal boundary layer thickness near the hot wall decreases.

#### What is beta in the Rayleigh number?

Rayleigh number, Ra, is a dimensionless term used in the calculation of natural convection. where g is acceleration due to gravity, β’ is coefficient of thermal expansion of the fluid, ΔT is temperature difference, x is length, ν is kinematic viscosity and κ is thermal diffusivity of the fluid.

**What is critical Reynolds number?**

1 Critical Reynolds Number. A critical Reynolds number is determined as a limit where the laminar flow changes to turbulent flow. If the calculated NRe is greater than the critical Reynolds number NRec, the flow regime is turbulent; otherwise the flow regime is laminar.

**What does high Schmidt number mean?**

The Schmidt number corresponds to the Prandtl number in heat transfer. A Schmidt number of unity indicates that momentum and mass transfer by diffusion are comparable, and velocity and concentration boundary layers almost coincide with each other.